Hydrogels are water-swollen networks of hydrophilic homopolymers or copolymers. These networks may be formed by various techniques; however, the most common synthetic route is the free radical polymerization of vinyl monomers in the presence of a difunctional cross-linking agent and a swelling agent. The resulting polymer exhibits both liquid-like properties, attributable to the major constituent, water, and solid-like properties due to the network formed by the cross-linking reaction. These solid-like properties take the form of a shear modulus that is evident upon deformation.
Hydrogels offer biocompatibility and have been shown to have reduced tendency for inducing thrombosis, encrustation and inflammation when used in medical devices. Unfortunately, the use of hydrogels in biomedical device applications has been hindered by limitations on the form and mechanical characteristics of the existing hydrogels. Many medical devices use hydrogels to improve device biocompatibility; however, many hydrogels can only be used in coatings. Many hydrogels suffer from low modulus, low yield stress, and low strength when compared to non-swollen polymer systems. Lower mechanical properties result from the swollen nature of hydrogels and the non-stress bearing nature of the swelling agent. Existing in situ cured hydrogels provide a benefit in that they can flow to fit a particular tissue, void, or lumen. However, these materials often lose that ability once they cure, and become subject to the drawbacks listed above. Fully cured hydrogels are easier to handle, but lack the shape-filling, conformable characteristics of the in situ curing systems.
Of particular note is that while the biocompatible and conformable characteristics of in situ cured hydrogels are desirable, the methods of applying in situ curing hydrogels are cumbersome. The restriction of keeping two or more reactive components separate from each other and stable during shipment and storage of devices of this type presents a significant burden on the user. Typically, the reactive components are stored apart from any reconstituting fluids in the device kits. At the point of use, the user is required to assemble multiple containers, reconstitute the materials, and transfer the reconstituted materials to a delivery system prior to applying the material. In some cases this process must be completed within a certain time limit to prevent loss of activity of the hydrogel material.
As such, there is a continuing need to develop new compositions capable of forming in situ biocompatible hydrogel structures that offer improved therapeutic outcomes.